The present invention relates to a U-shaped reaction tube for use in an automatic chemical analyzer and a method for manufacturing the same.
As described in U.S. Pat. No. 3,592,605, a known U-shaped reaction tube comprises a cup portion having a large radius for supplying sample and reagent therein, a substantially U-shaped tube portion having a small radius, one end being connected to the bottom of cup portion and a non-cupped end portion having a small radius connected to the other end of the U-shaped tube portion for connecting a pump therethrough, and these portions are integrally made of glass. The known tubes have been manufactured by a glass craft, and therefore, it is difficult to keep a manufacturing error within a predetermined accuracy range. Moreover, since openings of the cup and non-cupped end portions cannot be positioned accurately, it is not possible to discharge completely a sample solution or a washing liquid contained in the reaction tube.
Further, since the sample solution or the washing liquid is discharged through the opening of the non-cupped end portion under a vacuum suction pressure, it is necessary to connect a suction tube to the opening of the non-cupped end portion hermetically. To this end, it is necessary to polish the opening edge of the non-cupped end portion sufficiently or to arrange a resilient member at the tip of non-cupped end portion and thus, the reaction tube becomes expensive in cost and complicated in construction. Furthermore, since the U-shaped reaction tube is made of glass, it might break during use thereof. In the known analyzer, usually a plurality of U-shaped reaction tubes are secured by cement to a common mounting member and therefore, even if only one reaction tube is broken, the mounting member supporting a plurality of unbroken reaction tubes must be discarded, which results in a higher operating cost.
Moreover, a conventional U-shaped reaction tube made of glass has disadvantages that the glass itself has a hydrophilic property and is heavy in weight. That is to say, a washing liquid might remain on an inner wall of the test tube after washing to cause contamination between sample solutions. Further, a large number of the reaction tubes, such as three hundred, are arranged on a turret, resulting in the analyzer becoming heavy in weight and requiring a large driving mechanism for rotating the heavy turret.